1. Field of the Invention
The present invention relates to signal repeaters used in conjunction with a serial data line, and more particularly, to a signal repeater that is able to buffer variations in signal voltage.
2. Background Information
The Universal Serial Bus (USB) is a serial data line that supports data exchange between a host computer (USB host) and a wide range of simultaneously accessible peripherals (USB devices). The USB physical interconnect is a tiered star topology. A hub is at the center of each star. Each connection is a point-to-point connection between the USB host and a hub or a USB device, or a hub connected to another hub or USB device. FIG. 1 illustrates the topology of the USB. The USB host contains host controllers that provide access to the USB devices in the system.
The USB specification requires that USB devices be able to withstand voltages of up to 5.25 volts on their signal lines indefinitely. Although nominally, signaling on a USB connection should never exceed 5 volts, because of voltage spikes, reflections, short circuits in the connection, and other anomalies, the voltage on the USB connection may sometimes exceed 5 volts. Most current USB devices are built using 5 volt tolerant processes, therefore, this requirement in the USB specification is not problematic.
However, many semiconductor manufacturing companies are migrating to a 5 volt intolerant process. In other words, as process geometries move to 0.35 micron and lower, a 5.25 volt input to such an integrated device will prove catastrophic.
Currently, the most common solution for providing USB devices that can tolerate 5.25 volts on the signal lines is through the use of various forms of overvoltage crow bar circuits. However, the overvoltage crow bar circuits may not afford the necessary voltage protection and sometimes require routing a controlled impedance line through the integrated circuit.
A method that includes receiving bus signals having a first voltage from a serial data line. The bus signals are converted from the first voltage into a device signal having a second voltage. Finally, the device signal is provided to a device.